Recent advances in plant genetic engineering have opened new doors to engineer plants to have improved characteristics or traits, such as plant disease resistance, insect resistance, herbicidal resistance, yield improvement, improvement of the nutritional quality of the edible portions of the plant, and enhanced stability or shelf-life of the ultimate consumer product obtained from the plants. Thus, a desired gene (or genes) with the molecular function to impart different or improved characteristics or qualities can be incorporated properly into the plant's genome. The newly integrated gene (or genes) coding sequence can then be expressed in the plant cell to exhibit the desired new trait or characteristic. It is important that appropriate regulatory signals be present in proper configurations in order to obtain the expression of the newly inserted gene coding sequence in the plant cell. These regulatory signals typically include a promoter region, a 5′ non-translated leader sequence and a 3′ transcription termination/polyadenylation sequence.
A promoter is a non-coding genomic DNA sequence, usually upstream (5′) to the relevant coding sequence, to which RNA polymerase binds before initiating transcription. This binding aligns the RNA polymerase so that transcription will initiate at a specific transcription initiation site. The nucleotide sequence of the promoter determines the nature of the RNA polymerase binding and other related protein factors that attach to the RNA polymerase and/or promoter, and the rate of RNA synthesis.
It has been shown that certain promoters are able to direct RNA synthesis at a higher rate than others. These are called “strong promoters”. Certain other promoters have been shown to direct RNA synthesis at higher levels only in particular types of cells or tissues and are often referred to as “tissue specific promoters”, or “tissue-preferred promoters”, if the promoters direct RNA synthesis preferentially in certain tissues (RNA synthesis may occur in other tissues at reduced levels). Since patterns of expression of a chimeric gene (or genes) introduced into a plant are controlled using promoters, there is an ongoing interest in the isolation of novel promoters that are capable of controlling the expression of a chimeric gene (or genes) at certain levels in specific tissue types or at specific plant developmental stages.
Among the most commonly used promoters are the nopaline synthase (NOS) promoter (Ebert et al., Proc. Natl. Acad. Sci. U.S.A. 84:5745-5749 (1987)); the octapine synthase (OCS) promoter, caulimovirus promoters such as the cauliflower mosaic virus (CaMV) 19S promoter (Lawton et al., Plant Mol. Biol. 9:315-324 (1987)); the CaMV 35S promoter (Odell et al., Nature 313:810-812 (1985)), and the figwort mosaic virus 35S promoter (Sanger et al., Plant Mol. Biol. 14:433-43 (1990)); the light inducible promoter from the small subunit of rubisco (Pellegrineschi et al., Biochem. Soc. Trans. 23(2):247-250 (1995)); the Adh promoter (Walker et al., Proc. Natl. Acad. Sci. U.S.A. 84:6624-66280 (1987)); the sucrose synthase promoter (Yang et al., Proc. Natl. Acad. Sci. U.S.A. 87:4144-4148 (1990)); the R gene complex promoter (Chandler et al., Plant Cell 1:1175-1183 (1989)); the chlorophyll a/b binding protein gene promoter; and the like.
An angiosperm flower is a complex structure generally consisting of a pedicel, sepals, petals, stamens, and a pistil. A stamen comprises a filament and an anther in which the male gametophyte pollens reside. A pistil comprises a stigma, style and ovary. An ovary contains one or more ovules in which the female gametophyte embryo sac, egg cell, central cell, and other specialized cells reside. Flower promoters in general include promoters that direct gene expression in any of the above tissues or cell types. Lipid transfer protein (LTP) genes have been isolated from barley (Federico et al., Plant Mol. Biol. 57:35-51 (2005)), strawberry (Yubero-Serrano et al, J. Exp. Bot. 54:1865-1877 (2003)), Arabidopsis (Thoma et al., Plant Physiol. 105:35-45 (1994)), Norway spruce (Sabala et al., Plant Mol. Biol. 42:461-478 (2000)), rice (Vignols et al., Gene 142:265-270 (1994)), carrot (Toonen et al., Plant J. 12:1213-1221 (1997)), Brassica napus (Sohal et al., Plant Mol. Biol. 41:75-87 (1999)), Sorghum vulgare (Pelese-Siebenbourg et al., Gene 148:305-308 (1994)), and other plant species. The reported LTP genes are known to have various expression patterns in respective plants. However, there remains a lack of soybean LTP genes or flower-preferred expression of LTP genes. LTP assays have been described (Jean-Claude Kader, Annual Review of Plant Phys. and Plant Mol. Biol. 47: 627-654 (1996). Plant LTPs have eight cysteine residues located at conserved positions. The cysteine residues are engaged in four disulfide bridges (Jean-Claude Kader, Annual Review of Plant Phys. and Plant Mol. Biol. 47: 627-654 (1996)).
Although advances in technology provide greater success in transforming plants with chimeric genes, there is still a need for preferred expression of such genes in desired plants. Often times it is desired to selectively express target genes in a specific tissue because of toxicity or efficacy concerns. For example, flower tissue is a type of tissue where preferred expression is desirable and there remains a need for promoters that preferably initiate transcription in flower tissue. Promoters that initiate transcription preferably in flower tissue control genes involved in flower development and flower abortion.